From NBA.com:

Atlanta Hawks center Al Horford was held out of Sunday's game against the Philadelphia 76ers with a bone bruise in his right knee and will miss at least three more games.

Horford was injured in Friday's loss at Orlando and is out indefinitely after an MRI showed the bruise, coach Mike Woodson said.

The Hawks said before Sunday's game that Horford will not be with the team for a three-game road trip that begins Tuesday at Phoenix.